In the related art, on a refrigerant circuit formed by connecting an indoor unit and a hot water supply unit to a heat source unit by pipes, there exists a refrigeration cycle apparatus capable of indoor cooling operation and hot water supplying operation at the same time. In this system, a waste heat collecting operation that collects waste heat during indoor cooling as water-heating heat may be carried out, and highly efficient operation may be realized.
In the related art, in order to prevent refrigerant from flowing to an indoor unit (stopped unit) not conducting normal heating operation due to being stopped, set to ventilation mode, shut off by thermostat control, or the like, or a hot water supply unit (stopped unit) not conducting normal hot water supplying operation, a pressure-reducing mechanism is fully closed to prevent refrigerant from flowing. However, since the refrigerant flow rate is restricted, refrigerant accumulates in the heat exchangers installed in the units and the connecting pipes, causing operation with insufficient refrigerant in the refrigerant circuit of a refrigeration cycle apparatus. Although it is possible to prevent the accumulation of refrigerant in the heat exchangers and pipes by slightly opening the pressure-reducing mechanism and regulating the restriction of the refrigerant flow rate, the operating and environmental conditions are various, and reliably preventing the accumulation of refrigerant is difficult. It is also possible to prevent refrigerant accumulation by shutting off the inlet and outlet of the stopped unit with valves to set refrigerant inflow to zero, but refrigerant still flows in through structural gaps in the valves or the pressure-reducing mechanism, and reliably preventing the accumulation of refrigerant is difficult. For this reason, in the related art, technology that senses operation with insufficient refrigerant in the refrigeration cycle apparatus and collects refrigerant from the stopped unit has been developed (for example, see Patent Literature 1 and 2).